SSH Auth docs improvement

[k0dard]

Changes

Some small changes in the ssh auth part of the docs:

• Some commands concerning generating ssh keys were misleading (cat is used for viewing files and not generating ssh keys)
• Added formatting for ssh-privatekey and known-hosts keys
• Added instructions on how to get known-hosts value for GitHub

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• pre-commit Passed
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• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[linux-foundation-easycla]

• ✅login: k0dard / (b3a20af)
• ✅login: k0dard / (b3a20af, ebd6d6a)
• ✅login: k0dard / (b3a20af, ebd6d6a, be409f9)

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[tekton-robot]

Hi @k0dard. Thanks for your PR.

I'm waiting for a tektoncd member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[k0dard]

/kind documentation

[waveywaves]

/ok-to-test

[vdemeester]

One comment.
The 1. are so that we don't need to update all the numbers if we add one new item (it's a markdown feature 😛 )

[vdemeester]

This is an optional step though (one could use something else than GitHub)